Serum levels of soluble Fas ligand in patients with silicosis

Nonapoptotic functions of Fas/CD95 in the immune response

CD95 (also known as Fas) is a member of the tumor necrosis factor receptor (TNFR) superfamily. Its cognate ligand, CD95L, is implicated in immune homeostasis and immune surveillance. Mutations in this receptor are associated with a loss of apoptotic signaling and have been detected in an autoimmune disorder called autoimmune lymphoproliferative syndrome (ALPS) type Ia, which shares some clinical features with systemic lupus erythematosus (SLE). In addition, deletions and mutations of CD95 have been described in many cancers, which led researchers to initially classify this receptor as a tumor suppressor. More recent data demonstrate that CD95 engagement evokes nonapoptotic signals that promote inflammation and carcinogenesis. Transmembrane CD95L (m-CD95L) can be cleaved by metalloproteases, releasing a soluble ligand (s-CD95L). Soluble and membrane-bound CD95L show different stoichiometry (homotrimer versus multimer of homotrimers, respectively), which differentially affects CD95-mediated signaling through molecular mechanisms that remain to be elucidated. This review discusses the biological roles of CD95 in light of recent experiments addressing how a death receptor can trigger both apoptotic and nonapoptotic signaling pathways.

CD95/Fas, Non-Apoptotic Signaling Pathways, and Kinases

Endothelial cells lining new blood vessels that develop during inflammatory disorders or cancers act as doors that either allow or block access to the tumor or inflamed organ. Recent data show that these endothelial cells in cancer tissues and inflamed tissues of lupus patients overexpress CD95L, the biological role of which is a subject of debate. The receptor CD95 (also named Fas or apoptosis antigen 1) belongs to the tumor necrosis factor (TNF) receptor superfamily. Its cognate ligand, CD95L, is implicated in immune homeostasis and immune surveillance. Because mutations of this receptor or its ligand lead to autoimmune disorders such as systemic lupus erythematosus (SLE) and cancers, CD95 and CD95L were initially thought to play a role in immune homeostasis and tumor elimination via apoptotic signaling pathways. However, recent data reveal that CD95 also evokes non-apoptotic signals, promotes inflammation, and contributes to carcinogenesis; therefore, it is difficult to dissect its apoptotic effects from its non-apoptotic effects during pathogenesis of disease. CD95L is cleaved by metalloproteases and so exists in two different forms: a transmembrane form and a soluble ligand (s-CD95L). We recently observed that the soluble ligand is overexpressed in serum from patients with triple-negative breast cancer or SLE, in whom it contributes to disease severity by activating non-apoptotic signaling pathways and promoting either metastatic dissemination or accumulation of certain T cell subsets in damaged organs. Here, we discuss the roles of CD95 in modulating immune functions via induction of mainly non-apoptotic signaling pathways.

Alterations of Fas and Fas-Related Molecules in Patients with Silicosis

Persons with silicosis have not only respiratory disorders but also autoimmune diseases. To clarify the mechanisms involved in the dysregulation of autoimmunity found in patients with silicosis, we have been focusing on Fas and Fas-related molecules in the Fas-mediated apoptotic pathway, because Fas is one of the most important molecules regulating autoimmunity involving T cells. Our findings showed that patients with silicosis exhibited elevated serum soluble Fas levels, an increased relative expression of the soluble fas and dcr3 genes in peripheral blood mononuclear cells, high levels of other variant messages of the fas transcript, relatively decreased expression of genes encoding several physiological inhibitors (such as survivin and toso), and dominancy of lower-membrane Fas expressers in lymphocytes, which transcribe soluble fas dominantly, compared with soluble fas transcription in healthy donors. These findings are consistent with known features regarding immunological factors, such as serum immunogulobulin G levels and the titer of anti-nuclear autoantibodies in silicosis. In addition, anti-caspase 8 autoantibody and anti-Fas autoantibody were detected in serum specimens from patients with silicosis, and a functional assay showed that anti-Fas antibody stimulated Fas-mediated apoptosis. We hypothesize that there are two subpopulations of silicosis lymphocytes. One is a long-term surviving fraction that includes self-recognizing clones showing lower levels of membrane Fas and inhibition of Fas/Fas ligand binding in extracellular spaces. The other subpopulation exhibits apoptosis caused by silica and silicates, is recruited from bone marrow, shows higher levels of membrane Fas, and is sensitive to anti-Fas autoantibody. Further investigation should be performed to confirm the effects of silica and silicates on the human immune system.

The CD95/CD95L signaling pathway: a role in carcinogenesis

Apoptosis is a fundamental process that contributes to tissue homeostasis, immune responses, and development. The receptor CD95, also called Fas, is a member of the tumor necrosis factor receptor (TNF-R) superfamily. Its cognate ligand, CD95L, is implicated in immune homeostasis and immune surveillance, and various lineages of malignant cells exhibit loss-of-function mutations in this pathway; therefore, CD95 was initially classified as a tumor suppressor gene. However, more recent data indicate that in different pathophysiological contexts, this receptor can transmit non-apoptotic signals, promote inflammation, and contribute to carcinogenesis. A comparison with the initial molecular events of the TNF-R signaling pathway leading to non-apoptotic, apoptotic, and necrotic pathways reveals that CD95 is probably using different molecular mechanisms to transmit its non-apoptotic signals (NF-κB, MAPK, and PI3K). As discussed in this review, the molecular process by which the receptor switches from an apoptotic function to an inflammatory role is unknown. More importantly, the biological functions of these signals remain elusive.

Detection of anti-topoisomerase I autoantibody in patients with silicosis

OBJECTIVES

The aim of this study was to detect anti-topoisomerase I (anti-topo I) autoantibodies, which are known to be limited in systemic sclerosis patients, in silicosis patients with no clinical symptoms of autoimmune disease.

METHODS

Serum anti-topo I autoantibodies were detected using ELISA. Differences in clinical parameters between patients with and without anti-topo I autoantibodies were analyzed.

RESULTS

Seven of 69 patients had anti-topo I autoantibodies. These 7 patients showed elevated PaCO(2) values (P=0.0212), and inverse correlations between serum soluble Fas levels and PaCO(2) values were found.

CONCLUSION

Anti-topo I autoantibodies were detected in 10.1% of silicosis patients without any clinical symptoms of autoimmune disease. The findings here suggest that the genesis of anti-topo I autoantibodies might be related to pulmonary involvement or lung fibrosis associated with progression of silicosis.

Keynote lecture in the 13th Japanese Society of Immunotoxicology (JSIT 2006) : -Pathophysiological Development and Immunotoxicology: what we have found from research related to silica and silicate such as asbestos-

Silica and silicates may disturb immune functions such as autoimmunity and tumor immunity, because people who are exposed to the materials sometimes develop autoimmune and malignant diseases, respectively. Although silica-induced disorders of autoimmunity have been explained as adjuvant-type effects of silica, more precise analyses are needed and should reflect the recent progress in immunomolecular findings. A brief summary of our investigations related to the immunological effects of silica/asbestos is presented. Recent advances in immunomolecular studies led to detailed analyses of the immunological effects of asbestos and silica. Both affect immuno-competent cells and these effects may be associated with the pathophysiological development of complications in silicosis and asbestos-exposed patients such as the occurrence of autoimmune disorders and malignant tumors, respectively. In addition, immunological analyses may lead to the development of new clinical tools for the modification of the pathophysiological aspects of diseases such as the regulation of autoimmunity or tumor immunity using cell-mediated therapies, various cytokines, and molecule-targeting therapies. In particular, as the incidence of asbestos-related malignancies is increasing and such malignancies have been a medical and social problem since the summer in 2005 in Japan, efforts should be focused on developing a cure for these diseases to eliminate the nation wide anxiety about these malignancies.

CD95-mediated cell signaling in cancer: mutations and post-translational modulations

Apoptosis has emerged as a fundamental process important in tissue homeostasis, immune response, and during development. CD95 (also known as Fas), a member of the tumor necrosis factor receptor (TNF-R) superfamily, has been initially cloned as a death receptor. Its cognate ligand, CD95L, is mainly found at the plasma membrane of activated T-lymphocytes and natural killer cells where it contributes to the elimination of transformed and infected cells. According to its implication in the immune homeostasis and immune surveillance, and since several malignant cells of various histological origins exhibit loss-of-function mutations, which cause resistance towards the CD95-mediated apoptotic signal, CD95 has been classified as a tumor suppressor gene. Nevertheless, this assumption has been recently challenged, as in certain pathophysiological contexts, CD95 engagement transmits non-apoptotic signals that promote inflammation, carcinogenesis or liver/peripheral nerve regeneration. The focus of this review is to discuss these apparent contradictions of the known function(s) of CD95.

Apoptosis modulation as a promising target for treatment of systemic sclerosis

Diffuse systemic sclerosis (SSc) is a fatal autoimmune disease characterized by an excessive ECM deposition inducing a loss of function of skin and internal organs. Apoptosis is a key mechanism involved in all the stages of the disease: vascular damage, immune dysfunction, and fibrosis. The purpose of this paper is to gather new findings in apoptosis related to SSc, to highlight relations between apoptosis and fibrosis, and to identify new therapeutic targets.

An overview of caspase: Apoptotic protein for silicosis

Silicosis is a chronic lung disease characterized by granulomatous and fibrotic lesions, which occurs due to accumulation of respirable silica mineral particles. Apoptosis is an important phenomenon of cell death in silicosis. The relationship between silica dust and its exposure is well established. But, the complex chain of cellular responses, which leads to caspase activation in silicosis, has not been fully discovered. Caspase activation plays a central role in the execution of apoptosis. Silica-induced apoptosis of the alveolar macrophages could potentially favor a proinflammatory state, occurring in the lungs of silicotic patients, resulting in the activation of caspase prior to induction of the intrinsic and extrinsic apoptosis pathways. Recent studies indicated that apoptosis may involve in pulmonary disorders. This review summarizes the current knowledge about the underling mechanism of biochemical pathways in caspase activation that have been ignored so far in silicosis. In addition, caspase could be a key apoptotic protein that can be used as an effective biomarker for the study of occupational diseases. It may provide an important link in understanding the molecular mechanisms of silica-induced lung pathogenesis.

Dysregulation of the immune system caused by silica and asbestos

Silica and asbestos cause pneumoconioses known as silicosis and asbestosis, respectively, that are each characterized by progressive pulmonary fibrosis. While local effects of inhaled silica particles alter the function of alveolar macrophages and sequential cellular and molecular biological events, general systemic immunological effects may also evolve. One well-known health outcome associated with silica exposure/silicosis is an increase in the incidence of autoimmune disorders. In addition, while exposure to silica--in the crystalline form--has also been seen to be associated with the development of lung cancers, it remains unclear as to whether or not silicosis is a necessary condition for the elevation of silica-associated lung cancer risks. Since asbestos is a mineral silicate, it would be expected to also possess generalized immunotoxicological effects similar to those associated with silica particles. However, asbestos-exposed patients are far better known than silicotic patients for development of malignant diseases such as lung cancer and mesothelioma, and less so for the development of autoimmune disorders. With both asbestos and crystalline silica, one important dysregulatory outcome that needs to be considered is an alteration in tumor immunity that allows for silica- or asbestos- (or asbestos-associated agent)-induced tumors to survive and thrive in situ. In this review, the immunotoxicological effects of both silica and asbestos are presented and contrasted in terms of their abilities to induce immune system dysregulation that then are manifest by the onset of autoimmunity or by alterations in host-tumor immunity.

Ability of trichloroethylene metabolite to promote immune pathology is strain-specific

Chronic low-level exposure to the environmental pollutant trichloroethylene has been shown to promote autoimmune disease in association with CD4(+) T-lymphocyte activation in lupus-prone MRL(+/+) mice. One of the primary metabolites of trichloroethylene, trichloroacetaldehyde hydrate (TCAH), was similarly shown to increase the percentage of IFNgamma-producing CD4(+) T-lymphocytes when added to the drinking water of MRL(+/+) mice. In addition, TCAH-treated MRL(+/+) mice developed skin inflammation and alopecia. In the present study TCAH was tested for its ability to accelerate the development of alopecia in C3H/HeJ mice which tend to develop the disorder spontaneously late in life. In contrast to MRL(+/+) mice, C3H/HeJ mice treated with TCAH did not develop alopecia at an increased rate. In addition, TCAH did not promote the expansion of activated IFNgamma-producing CD4(+) T-lymphocytes in C3H/HeJ mice. CD4(+) T-lymphocytes from TCAH-treated C3H/HeJ mice, unlike their MRL(+/+) counterparts, did not become resistant to activation-induced apoptosis following in vivo exposure to TCAH. Taken together, it appears that the ability of TCAH to promote immune-mediated pathology is strain-specific and may require an autoimmune-prone genetic background.

Changes of cytokine production and cell viability of peripheral blood mononuclear cells from silicosis patients: effect of in vitro treatment with acetylsalicylic acid

In this study, IL-6 and IL-12p40 production and cell viability of peripheral blood mononuclear cells from silicosis patients after in vitro stimulation were investigated. Furthermore, the effects of introducing acetylsalicylic acid to stimulated patients’ peripheral blood mononuclear cells on cytokine production and cell viability were determined. Nine patients with moderate silicosis, 11 with severe silicosis and 14 healthy subjects were recruited for this study. The level of IL-6 produced by patients peripheral blood mononuclear cells decreased depending on the stage of the disease. The addition of acetylsalicylic acid had significantly suppressive effect on the IL-6 production by lipopolysaccharide—stimulated patients’ peripheral blood mononuclear cells. Acetylsalicylic acid treatment of C3 binding glycoprotein—stimulated patients’ peripheral blood mononuclear cells led to significant upregulation of IL-12p40 production. Results showed a stage-dependent decrease of cell viability of peripheral blood mononuclear cells from silicosis patients. Acetylsalicylic acid significantly decreased cell viability entirely in stimulated peripheral blood mononuclear cells from patients with severe silicosis. In conclusion, this study showed that the disease progression affects peripheral blood mononuclear cells in patients with silicosis and causes functional changes that became apparent after stimulation. Our study demonstrated that in severe silicosis the treatment with acetylsalicylic acid, as an anti-inflammatory agent, might not be beneficial for patients.

Cytokine alteration and speculated immunological pathophysiology in silicosis and asbestos-related diseases

This review is partly composed of the presentation "Cytokine alteration and speculated immunological pathophysiology in silicosis and asbestos-related diseases" delivered during the symposium "Biological effects of fibrous and particulate substances and related areas" organized by the Study Group of Fibrous and Particulate Studies of the Japanese Society of Hygiene and held at the 78th Annual Meeting in Kumamoto, Japan. In this review, we briefly introduce the results of recent immunological analysis using the plasma of silica and asbestos-exposed patients diagnosed with silicosis, pleural plaque, or malignant mesothelioma. Thereafter, experimental background and speculation concerning the immunological pathophysiology of silica and asbestos-exposed patients are discussed.

Serum neopterin in workers exposed to inorganic dust containing free crystalline silicon dioxide

The study was conducted among 92 male workers, divided into two groups depending on workplace and level of inorganic dust containing free crystalline SiO2 in the work environment, and 43 healthy workers without exposure to dust aerosols. The measured inhalable and respirable dust concentrations, as well as the concentration of free crystalline silica (FCS) in the respirable fraction were different for the two groups, but the percentage of free crystalline silica in the respirable fraction was almost identical. Significantly higher neopterin levels were found in workers exposed to dust, compared to the control group: 12.72 nmol/L and 6.32 nmol/L respectively (p<0.05). No significant difference was found between serum neopterin levels in both groups of the exposed workers. Among the groups with different length of service, a statistically higher neopterin level was evident only in the workers with length of service less than 10 years (p<0.05). The correlation analysis did not find a significant dependence of neopterin levels on the age of the studied workers or on the duration of smoking in packet years. The difference between neopterin levels in smokers and non-smokers was nonsignificant. The results obtained show that increased neopterin levels in the exposed workers are not influenced by individual features, duration and level of exposure to inorganic dust, but mostly by the presence of FCS in the respirable fraction.

Soluble Interleukin-2 Receptor as an Indicator of Immunological Disturbance Found in Silicosis Patients

Silicosis patients (SILs) possess not only respiratory disorders but also alterations in autoimmunity. To determine an early indicator of immunological disturbance in SILs, the role of serum-soluble interleukin (IL)-2 receptor (sIL-2R) was analyzed. Of ten SILs, immunological clinical parameters such as immunoglobulin (Ig) G, complements, the titer of autoantibodies including anti-nuclear antibodies (ANA), anti-Scl-70 antibody (Ab) and anti-centromere (CM) Ab, and experimental indicators such as serum-soluble Fas, serum IL-2, CD25+ cells in CD4+ or CD8+ fractions, and sIL-2R were divided from respiratory parameters such as % vital capacity (%VC), percentage of forced expiratory volume in 1 second (FEV1.0%) and v25/Ht (liter/second/m(body height) by a correlation assay. Additionally, a stepwise regression test showed that sIL-2R was correlated with Ig G, ANA and anti-CM Ab. Furthermore, factor analysis revealed that sIL-2R contributed to the subpopulation of SILs with poorer immunological status in the absence of alterations in respiratory status. By defining healthy donors as 1, SILs as 2 and patients with systemic sclerosis as 3 for immunopathological progression status as metric variables, sIL2R and ANA showed a strong positive correlation. This suggests that sIL-2R is a good clinical indicator of immunological disturbance found in SILs without clinical manifestations of any disturbance in autoimmunity. Further analysis using a large-scale number of patients should be performed to confirm these findings.

Increased soluble Fas ligand levels in patients with Stevens-Johnson syndrome and toxic epidermal necrolysis preceding skin detachment

BACKGROUND

It is difficult to distinguish the early phase of Stevens-Johnson syndrome (SJS)/toxic epidermal necrolysis (TEN) from other ordinary types of drug-induced skin reactions (ODSRs). Levels of several serum soluble factors, including soluble Fas ligand (sFasL), have been reported to be increased in patients with SJS/TEN; however, the marker to predict the onset of SJS/TEN before the development of skin detachment or mucosal lesions has not been identified.

OBJECTIVE

We sought to determine whether sFasL might be a useful marker in the early stages of SJS/TEN.

METHODS

Sera of 19 patients with SJS and 16 patients with TEN at 1 or multiple time points were obtained from Japanese multiple hospitals. The disease onset (day 1) was defined when erosion/ulceration of the mucocutaneous or ocular lesion first developed. For the investigation of soluble factors, including sFasL, TNF-alpha, IFN-gamma, IL-6, and sCD40 ligand, we used ELISAs and Cytometric Bead Arrays.

RESULTS

Before disease onset (day -4 to approximately -2), 7 samples were available, and we detected the highest concentrations of sFasL in 5 (71.4%) of 7 patients. Increased sFasL levels decreased rapidly within 5 days of disease onset. In all 32 patients with ODSRs and 33 healthy control subjects, no increase of sFasL levels was detected. Other soluble factor concentrations did not show significant difference with those seen in patients with SJS/TEN before disease onset and ODSRs.

CONCLUSION

The sFasL levels of sera in patients with SJS/TEN are significantly increased before development of skin detachment, mucosal lesions, or both.

Silica-associated systemic lupus erythematosus in an elderly man

The predominantly young woman-orientated systemic lupus erythematosus (SLE) is a disease that involves an extremely complicated and multifactorial interaction of various genetic and environmental factors. Crystalline silica (Si) may act as an immunoadjuvant to increase secretions of inflammatory endogenous substances and antibody production. In addition, previous studies have suggested that exposure to Si may induce SLE. Although the biologic mechanism of Si in SLE is unclear, defective apoptosis leading to the prolonged survival of pathogenic lymphocytes was thought to be one of mechanisms of Si-associated SLE (sSLE). In the present study, a rare case of an elderly man suffering from sSLE responded well to glucocorticoid therapy. The present findings were reviewed with reference to previous literature.

Reduced function of CD4+25+ regulatory T cell fraction in silicosis patients

The quality and quantity of CD4+25+ regulatory T cells (Treg) in silicosis patients (SIL) were examined and compared with results from healthy donors (HD) because SIL often develop autoimmune diseases along with pulmonary disorders. Peripheral blood mononuclear cells from 57 SIL and 50 HD were analyzed for Treg. Treg frequency and clinical parameters were subjected to a factor analysis. Treg and CD4+25- T cells (Tneg) from five HD and five SIL, sorted by flow-cytometer, were used for functional assays of Treg, the expression pattern of Treg specific genes (FoxP3, GITR and CTLA-4) and activation-related genes (CD122 and CD123). Although the actual frequency of Treg did not differ between SIL and HD, the age-corrected level was reduced in SIL. The factor analysis showed that Treg frequency was positively associated with the serum level of IL-2. The inhibitory effect of Treg on Tneg activation was decreased when the Treg:Tneg ratio was 1:1/4 to 1/2. In addition, Treg dominancy of FoxP3 and CTLA-4 expression and Tneg dominancy of CD132 expression found in HD were lost in SIL. These results indicated that the Treg fraction in SIL may be substituted with chronically activated T cells due to recurrent exposure to silica, resulting in a reduction in the frequency and function of Treg. Since the reduction of Treg may precede the clinical manifestation, as silicosis may be a pre-clinical status for autoimmune diseases, control of Treg function using cell and/or gene therapy may be a good way to manage autoimmune disease.

Apoptosis and extracellular matrix remodelling in human silicosis

AIMS

Silicosis is a chronic occupational disease caused by the inhalation of free crystalline silica particles which produce inflammation and tissue destruction followed by remodelling of the extracellular matrix. Apoptosis has been implicated in the development of the initial inflammation that triggers the remodelling process. Our aim was to elucidate the importance of Fas-ligand (Fas-L) in this disorder and to study the relationship between Fas-L and several other inflammatory and fibrotic remodelling markers.

METHODS AND RESULTS

We analysed 23 lung biopsies from silicotic patients and five controls, quantifying Fas-L and Bcl-2 expression by inflammatory cells as well as mast cells and collagen and elastic fibres. We used immunohistochemistry and morphometry to evaluate the amount of Fas-L and Bcl-2. Our analysis revealed that the silicotic lung stage was significantly related to Fas-L, mast cell and extracellular matrix remodelling. Fas-L expression was inversely associated with mast cells, collagen/elastic deposition and the silicotic lung.

CONCLUSION

Fas-L, mast cell staining and collagen/elastic fibre quantities in silicotic lungs are strongly related to silicosis progression.

Mechanistically identified suitable biomarkers of exposure, effect, and susceptibility for silicosis and coal-worker's pneumoconiosis: a comprehensive review

Clinical detection of silicosis is currently dependent on radiological and lung function abnormalities, both late manifestations of disease. Markers of prediction and early detection of pneumoconiosis are imperative for the implementation of timely intervention strategies. Understanding the underlying mechanisms of the etiology of coal workers pneumoconiosis (CWP) and silicosis was essential in proposing numerous biomarkers that have been evaluated to assess effects following exposure to crystalline silica and/or coal mine dust. Human validation studies have substantiated some of these proposed biomarkers and argued in favor of their use as biomarkers for crystalline silica- and CWP-induced pneumoconiosis. A number of "ideal" biological markers of effect were identified, namely, Clara cell protein-16 (CC16) (serum), tumor necrosis factor-alpha (TNF-alpha) (monocyte release), interleukin-8 (IL-8) (monocyte release), reactive oxygen species (ROS) measurement by chemiluminescence (neutrophil release), 8-isoprostanes (serum), total antioxidant levels measured by total equivalent antioxidant capacity (TEAC), glutathione, glutathione peroxidase activity, glutathione S-transferase activity, and platelet-derived growth factor (PDGF) (serum). TNF-alpha polymorphism (blood cellular DNA) was identified as a biomarker of susceptibility. Further studies are planned to test the validity and feasibility of these biomarkers to detect either high exposure to crystalline silica and early silicosis or susceptibility to silicosis in gold miners in South Africa.

Exposure to a metabolite of the environmental toxicant, trichloroethylene, attenuates CD4+ T cell activation-induced cell death by metalloproteinase-dependent FasL shedding

Long-term exposure to the environmental contaminant trichloroethylene (TCE) in drinking water has been shown to promote autoimmune disease in association with the expansion of activated CD4+ T cells. The effects of TCE on CD4+ T cells were linked in the present study to the ability of TCE metabolite, trichloroacetaldehyde hydrate (TCAH), to inhibit activation-induced cell death (AICD) in CD4+ T cells. TCAH attenuated AICD in CD4+ T cells by decreasing FasL (CD178) expression but not by altering Fas (CD95) expression or by interfering with Fas-signaling events following direct engagement of the Fas receptor. The TCAH-induced decrease in FasL expression did not appear to be mediated at the transcriptional level but was instead due to increased shedding of FasL from the surface of the CD4+ T cells. The ability of TCAH to cleave FasL and thereby decrease AICD appeared to be mediated by metalloproteinases and correlated with a TCAH-induced increase in matrix metalloproteinase-7. Thus, this study presents the novel finding that the environmental contaminant TCE works via its metabolite TCAH to attenuate AICD by increasing metalloproteinase activity that cleaves FasL from CD4+ T cells. This represents a mechanism by which an environmental trigger inhibits AICD in CD4+ T cells and may thereby promote CD4+ T cell-mediated autoimmune disease.

Silica exposure is associated with increased risk of developing rheumatoid arthritis: results from the Swedish EIRA study

OBJECTIVE

To study the association between silica exposure and rheumatoid arthritis and how it is modified by cigarette smoking.

METHODS

Data were analysed from 276 male cases and 276 male controls aged 18 to 70 years, included in a Swedish population based study between May 1996 and June 2001. A case was defined as a person recently diagnosed with rheumatoid arthritis according to the ACR criteria. Controls were selected from the study base as a stratified random sample accounting for age, sex, and residency. Men with a self reported history of work with rock drilling, stone crushing, or exposure to stone dust in general were defined as silica exposed. Rheumatoid factor (RF) status among cases was recorded.

RESULTS

Silica exposed men had increased risk of rheumatoid arthritis, with an odds ratio (OR), adjusted for age, residential area, and smoking, of 2.2 (95% confidence interval, 1.2 to 3.9) among men aged 18 to 70 years, and 2.7 (1.2 to 5.8) among those aged 50 to 70 years. Men who had worked with rock drilling or stone crushing (regarded as highly exposed) had a slightly greater increase in risk of rheumatoid arthritis than silica exposed men in general, with an OR of 3.0 (1.2 to 7.6). The joint effects of silica exposure and smoking were compatible with synergy between these two exposures in the development of rheumatoid arthritis but this was not conclusive.

CONCLUSIONS

Silica exposure is associated with increased risk of developing rheumatoid arthritis. This association is not explained by smoking habits.

Expression of Fas antigen and Fas ligand in bronchoalveolar lavage from silicosis patients

OBJECTIVE

To understand the role of apoptosis through Fas/Fas ligand (FasL) interaction in the pathogenesis of silicosis, we examined the expression of Fas antigen, FasL and apoptosis in bronchoalveolar lavage fluid lymphocytes obtained from patients with silicosis.

MATERIALS AND METHODS

Ten patients with silicosis, and 10 healthy controls were studied. Non-adherent cells were separated and analysed by cytometry for the expression of Fas antigen, FasL, and the co-expression of Fas/FasL. By double staining, we studied the FasL expression on CD4, CD8, CD56 and CD45RO-positive cells. DNA fragmentation was investigated by the terminal deoxy(d) UTP nick end labelling (TUNEL) method.

RESULTS

We have found Fas and FasL expression in silicosis patients to be significantly higher than those in healthy controls. Interestingly, 6-18% of lymphocytes from silicosis patients co-expressed Fas and FasL. In silicosis patients, FasL was highly expressed on CD4+, CD56+ and CD45RO+ bronchoalveolar lavage cells. Fas antigen expressing cells showed DNA fragmentation characteristic for apoptosis.

CONCLUSION

FasL was significantly expressed on cytotoxic effector and memory cells. The Fas/FasL system is implicated in the inflammatory process observed in silicosis patients.

Evaluation of caspase 1 and sFas serum levels in patients with systemic sclerosis: correlation with lung dysfunction, joint and bone involvement

Recent studies point out at the role of apoptosis disturbances in the development of systemic sclerosis(SSc). The aim of our study was to examine caspase 1 and sFas serum levels in scleroderma patients and correlate the obtained results with skin involvement and internal organ changes. We studied 29 patients (14 with limited and 15 with diffuse SSc). The extension of skin involvement was measured using Total Skin Score (TSS). Internal organ involvement was assessed by specialist procedures. Serum caspase 1 and sFas levels were measured by enzyme-linked immunosorbent assay. We found correlation between sFas serum level and duration of Raynaud's phenomenon and TSS; caspase 1 serum level correlated only with TSS. Correlations between caspase 1 and lung dysfunction and sFas levels with joint and bone involvement in SSc patients were also observed. The obtained results revealed that disturbances of apoptosis might play a role in SSc pathogenesis. Caspase 1 and sFas serum levels correlate with the skin involvement severity, lung dysfunction, joint and bone changes.

Silica exposure and systemic vasculitis

Work in Department of Energy (DOE) facilities has exposed workers to multiple toxic agents leading to acute and chronic diseases. Many exposures were common to numerous work sites. Exposure to crystalline silica was primarily restricted to a few facilities. I present the case of a 63-year-old male who worked in DOE facilities for 30 years as a weapons testing technician. In addition to silica, other workplace exposures included beryllium, various solvents and heavy metals, depleted uranium, and ionizing radiation. In 1989 a painful macular skin lesion was biopsied and diagnosed as leukocytoclastic vasculitis. By 1992 he developed gross hematuria and dyspnea. Blood laboratory results revealed a serum creatinine concentration of 2.1 mg/dL, ethrythrocyte sedimentation rate of 61 mm/hr, negative cANCA (antineutrophil cytoplasmic antibody cytoplasmic pattern), positive pANCA (ANCA perinuclear pattern), and antiglomerular basement membrane negative. Renal biopsy showed proliferative (crescentric) and necrotizing glomerulonephritis. The patient's diagnoses included microscopic polyangiitis, systemic necrotizing vasculitis, leukocytoclastic vasculitis, and glomerulonephritis. Environmental triggers are thought to play a role in the development of an idiopathic expression of systemic autoimmune disease. Crystalline silica exposure has been linked to rheumatoid arthritis, scleroderma, systemic lupus erythematosus, rapidly progressive glomerulonephritis and some of the small vessel vasculitides. DOE workers are currently able to apply for compensation under the federal Energy Employees Occupational Illness Compensation Program (EEOICP). However, the only diseases covered by EEOICP are cancers related to radiation exposure, chronic beryllium disease, and chronic silicosis.

Silica-induced apoptosis in murine macrophage: involvement of tumor necrosis factor-alpha and nuclear factor-kappaB activation

Alveolar macrophages play a critical role in silica-induced lung fibrosis. Silica exposure induces tumor necrosis factor (TNF)-alpha release and nuclear factor (NF)-kappaB activation, and apoptotic mechanisms have been implicated in silica-induced pathogenesis. To characterize potential relationships between these signaling events, we studied their induction in two murine macrophage cell lines. The RAW 264.7 macrophage cell line was more sensitive, and the IC-21 macrophage cell line more tolerant to silica exposure (0.2 or 1 mg/ml for 6 h) as evidenced by significantly higher apoptotic responses in RAW 264.7 (P < 0.05). RAW 264.7 macrophages exhibited enhanced TNF-alpha production and NF-kappaB activation in response to silica, whereas IC-21 macrophages did not produce TNF-alpha in response to silica and did not induce NF-kappaB nuclear binding. Inhibition of NF-kappaB in RAW 264.7 cells with BAY11-7082 significantly increased apoptosis while inhibiting TNF-alpha release. In addition, TNF-alpha and NF-kappaB activation, but not apoptosis, were induced by lipopolysaccharide (LPS) in both cell lines, and NF-kappaB inhibition reduced LPS-induced TNF-alpha release. These data suggest that TNF-alpha induction is dependent on NF-kappaB activation in both cell lines. However, silica can induce apoptosis in murine macrophages, independently of TNF-alpha stimulation, as in IC-21 macrophages. Furthermore, NF-kappaB activation in macrophages may play dual roles, both pro- and antiapoptotic during silica injury.

Apoptosis underlies immunopathogenic mechanisms in acute silicosis

We investigated immunopathogenic roles for apoptosis in acute murine silicosis. Intratracheal silica instillation induced pulmonary inflammation and enlarged thoracic lymph nodes. Lymphocytes from silica-exposed lymph nodes showed reduced mitogenic responses to T cell receptor (TCR) stimulation, and markedly increased activation-induced cell death, compared with control lymphocytes from saline-exposed lymph nodes. CD4(+) T cell death was mediated by Fas ligand, because CD4(+) T cells from Fas ligand-deficient gld mice did not undergo activation-induced apoptosis. Silica deposition also resulted in increased apoptosis associated with inflammatory infiltrates in lung parenchyma. In vivo treatment with caspase inhibitors reduced neutrophil accumulation, and alleviated inflammation in the lungs of silica-treated mice. These results suggest that silica-induced apoptosis plays an inflammatory role in the lung parenchyma, and creates immunologic abnormalities in regional lymph nodes, with pathogenic implications for the host.

Elevated HGF levels in sera from breast cancer patients detected using a protein microarray ELISA

We developed an ELISA in high-density microarray format to detect hepatocyte growth factor (HGF) in human serum. The microassay can detect HGF at sub-pg/mL concentrations in sample volumes of 100 microL or less. The microassay is also quantitative and was used to detect elevated HGF levels in sera from recurrent breast cancer patients. The microarray format provides the potential for high-throughput quantitation of multiple biomarkers in parallel, as demonstrated with a multiplex analysis of five biomarker proteins.

Lymphopenia in occupational pulmonary silicosis with or without autoimmune disease

An increased prevalence of autoimmune diseases such as rheumatoid arthritis has been demonstrated in silica-exposed patients. The aim of this study was to determine the peripheral blood lymphocyte phenotype in a population of silicotic workers employed in the slate mines of the district. Silicosis was assessed in 58 patients according to the International Labor Office's criteria. Clinical and biological data including flow cytometric evaluation of the lymphocyte subsets were compared with those from 41 healthy volunteers. The silicotic patients had a higher prevalence of autoimmune diseases (6/58 versus 0/41: P < 0.05) and of elevated antinuclear antibody titres compared to the control group. A very significant decrease of total lymphocyte count (P < 0.001) involving B, T and Natural Killer cells was found in silicotic patients as compared with matched healthy volunteers. A significant increase in the percentage of activated T cells (12.3%) was observed in the silicotic group as compared to 6.5% in the control group (P = 5 x 10(-5)). Our results show that in silicotic patients, the absolute number of circulating lymphocytes is diminished with an increased proportion of activated T cells. Whether these findings could predispose to the development of autoimmune disorders is discussed.

Fas ligand triggers pulmonary silicosis

We investigated the role of Fas ligand in murine silicosis. Wild-type mice instilled with silica developed severe pulmonary inflammation, with local production of tumor necrosis factor (TNF)-alpha, and interstitial neutrophil and macrophage infiltration in the lungs. Strikingly, Fas ligand-deficient generalized lymphoproliferative disease mutant (gld) mice did not develop silicosis. The gld mice had markedly reduced neutrophil extravasation into bronchoalveolar space, and did not show increased TNF-alpha production, nor pulmonary inflammation. Bone marrow chimeras and local adoptive transfer demonstrated that wild-type, but not Fas ligand-deficient lung macrophages recruit neutrophils and initiate silicosis. Silica induced Fas ligand expression in lung macrophages in vitro and in vivo, and promoted Fas ligand-dependent macrophage apoptosis. Administration of neutralizing anti-Fas ligand antibody in vivo blocked induction of silicosis. Thus, Fas ligand plays a central role in induction of pulmonary silicosis.